Dual-SIM dual-standby terminals and multi-SIM multi-standby terminals are now launched, driven by rapid development of communications technologies and people's increasingly higher requirements on communications devices. A dual-SIM dual-standby terminal can be equipped with two user identity cards, for example, a user identity module (User identity module, UIM) card, or a universal subscriber identity module (Universal Subscriber Identity Module, USIM) card, or a subscriber identity module (Subscriber Identity Module, SIM) card, and both of the user identity cards are in a standby state. In a multi-SIM multi-standby terminal, user identity cards are further added to a dual-SIM dual-standby terminal, and all these user identity cards can be in a standby state at the same time.
In the prior art, it is necessary to develop a new set of software source code that supports functions of user identity cards of a multi-SIM multi-standby terminal, so as to support operation of the user identity cards in the multi-SIM multi-standby terminal. The prior art has the following disadvantages: (1) due to long software development cycle, defects in code cannot be rapidly fixed after the code is developed, and product software that meets subscriber requirements cannot be rapidly made available; (2) a new set of multi-SIM multi-standby source code is developed in addition to existing software source code that supports functions of a user identity card of a one-card one-standby terminal, the two sets of product code cannot be merged, and therefore, the two sets of code need to be maintained separately, which increases difficulty and cost of code maintenance. This problem not only exists in code maintenance of a multi-SIM multi-standby terminal, but also exists in other multi-instance software applications.